Emails marked as Junk in Outlook

Hi guys

I'm using Subscribe by Email on our campany's intranet with Buddypress to notify staff of new posts. Emails sent to users are marked as Junk by Outlook.

What can I do to prevent the messages being marked as spam? Our company uses Exchange 2010 with Active Directory. Our IT department says that every user would have to mark the message as Not Junk, but this doesn't solve the original problem.

Any ideas would be appreciated.

Kind regards